Microporous Gallophosphate Research Articles

Synthesis of microporous gallophosphates obtained by in situ decomposition of hexamethylphosphoramide

This work focuses on the development of a new synthesis route of reducing the number of reactants for the synthesis of phosphate-based materials. Thus one compound, the hexamethylphosphoramide, plays the roles of both precursor of the structure-directing agent (SDA) and the phosphorus source. The influence of some synthesis parameters (heating temperature, nature of solvent, acidity of the medium...) on the in situ decomposition of hexamethylphosphoramide and the results obtained for the gallophosphate system are reported.Syntheses were performed in aqueous or quasi non-aqueous (ethylene glycol) media at 150°C and 180°C. Samples were characterized by X-ray diffraction, liquid NMR spectroscopy (1H, 31P) and chemical analysis. 1H liquid NMR spectroscopy was used to fully characterize the decomposition of the alkylphosphoramide during the synthesis. The in situ generation of the SDA and the phosphorus source allowed preparing crystallized gallophosphates such as GaPO4-21, 2D-GAPON, 3D-GAPON, ULM-4 and ULM-3. Finally for the different reaction media, a decomposition mechanism of the hexamethylphosphoramide was proposed.

Characterization of the gel phases formed in the synthesis of microporous gallophosphate, cloverite

This work examines the formation of a microporous gallophosphate with an extra large pore system, namely cloverite (structure type: CLO) in fluoride medium. The amorphous gallophosphate gel containing the key precursor to cloverite was characterized and its evolution followed by 31P, 71Ga, 19F and 1H MAS NMR and several dipolar-coupling based double-resonance methods including 31P{71Ga} and 19F{71Ga} rotational-echo adiabatic passage double-resonance (REAPDOR), 31P{19F} and 19F{31P} rotational-echo double-resonance (REDOR), and 1H{31P} REDOR and 1H{71Ga} transfer of populations in double-resonance (TRAPDOR). The results indicate that upon mixing the Ga and P sources in the presence of structure directing agent (SDA) and HF, an amorphous oxyfluorinated gallophosphate precursor containing single 4-rings (4Rs) with alternating Ga–O–P linkage forms immediately. The Ga in the 4R is 6-coordinated and the two Ga in the 4R are bridged by a fluorine. Heating quickly converts the 4Rs to double four-membered rings (D4Rs), from which the entire CLO structure is built. The amount of the D4R rapidly increases with increasing heating time. The presence of fluoride ions greatly facilitates the formation of the 4Rs via bridging two Ga sites and the hydrothermal treatment promotes D4Rs via condensation. Interaction between SDA molecule and the phosphorus site in the gel is also probed. Further, the local structure of Ga sites in cloverite is characterized by 71Ga MAS NMR at ultrahigh magnetic field of 21.1 T by obtaining their electric field gradient tensor parameters.

Synthesis of a new microporous gallophosphate obtained by in situ generation of cyclohexylamine

A novel gallophosphate [Ga 13(PO 4) 18(C 6H 14N) 13(C 6H 13N)•2H 3O +•3H 2O] was synthesized using cyclohexylformamide as main solvent. The structure-directing agent is the cyclohexylamine which is generated in situ by thermal decomposition of the solvent. The structure was solved by single-crystal X-ray diffraction (space group P - 3 , a = 16.605 ( 14 ) Å , c = 17.22 ( 2 ) Å , Z = 1 , V = 4112 ( 6 ) Å 3 ). The 2D structure of Mu-30 is built up from (4,6) layers constituted of PO 4 tetrahedra sharing three of their oxygen atoms with one GaO 6 octahedron and two GaO 4 tetrahedra. Monoprotonated cyclohexylamine, water molecules and H 3O + ion are intercalated between the layers. Characterizations of this new gallophosphate by bulk chemical analysis, scanning electron microscopy, thermal analysis, and 13C and 31P solid state NMR spectroscopies are also reported.

Distribution of cobalt atoms in microporous gallophosphates: first approach by 31P NMR spin echo mapping

Three microporous cobaltgallophosphates, IM-6, CoGaPO 4-5 and GCP-EDI2 are characterized by 31P NMR spin echo mapping (SEM) experiments. These original analyses for metallophosphates reveal aggregations of Co in the first sphere of coordination of P (taking into account only T elements (Co, P, Ga)), and complete X-ray diffraction data. This study shows that the paramagnetic effect of Co is more important in CoAPOs than in CoGaPOs.

Incorporation of heteroatoms (Me=Zn, Co, Mn) into framework sites of the gallophosphate molecular sieve ULM-5

Zinc-, cobalt- and manganese-containing microporous gallophosphates (GaPOs) with the ULM-5 structure have been hydrothermally synthesized in the presence of fluoride ions and 1,6-diaminohexane as the structure-directing agent. X-ray diffraction, elemental and thermogravimetric analyses of ULM-5 and MeULM-5 (Me=Zn, Co, Mn) indicated the incorporation of 2 wt.% for Zn, 1 wt.% for Co and 0.5 wt.% for Mn into the GaPO framework. The UV–VIS spectrum collected on the as-synthesized CoULM-5 sample revealed five-coordinated cobalt(II) in the structure. X-ray absorption spectroscopy (EXAFS) showed that zinc(II), cobalt(II) and manganese(II) substituted gallium on non-tetrahedral sites in the MeULM-5 framework and revealed structural changes of ULM-5 and MeULM-5 in the calcination process. The template-free samples are not thermally stable in the ambient atmosphere.

Synthesis and Characterization of the New Hydroxygallophosphate Mu-18 with a Framework Topology Closely Related to That of the Hydroxyaluminophosphate AlPO4-EN3

A new three-dimensional microporous gallophosphate, named Mu-18, was obtained by hydrothermal synthesis in the presence of 1-methylpiperazine as an organic template. Its structure was determined by single-crystal X-ray diffraction. The symmetry is orthorhombic, space group Aba2 (No. 41), with a = 18.035(18) A, b = 10.513(11) A, and c = 14.293(11) A. The framework, closely related to that of the aluminophosphate AlPO 4 -EN3, displays a one-dimensional channel system delimited by eight-membered ring openings. This new hydroxygallophosphate was characterized by XRD, SEM, elemental and thermal analyses, and 13 C and 31 P solid-state NMR spectroscopy.

Trapping of an activated HF molecule inside a double four-ring unit: a quantum chemical model of the microporous fluorinated gallium phosphate ULM-18.

The penetration of a proton into the prenucleation building unit of a microporous gallophosphate and its interaction with an encapsulated fluorine anion have been investigated by means of DFT calculations. The inorganic part of the fluorinated gallophosphate ULM-18 has been modeled by a neutral, double four-ring (D4R) unit of formula [(GaOH)4(HPO4)4-H2O] encapsulating the fluorine ion. Assuming the cage to be rigid and to retain throughout the calculations the geometry determined from X-ray diffraction (XRD), the position of F(-) has been optimized, either as an isolated guest species or in the presence of an incoming proton. In agreement with the XRD structure, the fluorine atom has been shown to occupy in both cases a nonsymmetric position in the cage, being attached to three gallium atoms out of four. The distribution of the molecular electrostatic potential inside and outside the (F(-))@[(GaOH)4(HPO4)4-H2O] system has provided indications concerning the pathways that could be used by an incoming proton to penetrate the D4R unit and to approach the fluorine anion. The migration of a proton from an external site of fixation to the interior of the D4R unit has been found possible through two faces out of six. In both cases, the process has been found exothermic by approximately 0.17 eV and the energy barrier was estimated to approximately 0.8 eV. Inside the gallophosphate cage, the proton first adopts a position typical of a strong F...H...O bond made possible through an important shift of the fluorine anion away from the tripod of bonded gallium atoms. Then, the F(-)...H(+) system can easily evolve back and forth on a flat potential curve between one of the F...H...O bonded conformations and a situation characterized by the cleavage of the H...O link and the formation of a moderately activated F-H molecule, with the fluorine still attached to three gallium atoms.

Synthesis and characterization of the new microporous gallophosphate Mu-8

A new three-dimensional microporous gallophosphate named Mu-8 was hydrothermally synthesized in the presence of N, N, N ′, N ′-tetramethylethylenediamine as organic template. Its structure was determined from X-ray powder data by direct methods and subsequently refined using the Rietveld method. The symmetry is monoclinic, space group P2 1/c with a=9.513(9) Å, b=9.0486(1) Å, c=17.490(2) Å and β=114.7°(3). The structure consists of gallophosphate chains of edge-sharing four rings which are connected through PO 4 tetrahedra and GaO 5 pentahedra. The resulting framework contains channels along [1 0 0] which are delimited by eight-membered ring openings. This material was also characterized by thermal analysis, 13C and 31P solid state NMR spectroscopy.

Time-Resolved In-Situ Energy and Angular Dispersive X-ray Diffraction Studies of the Formation of the Microporous Gallophosphate ULM-5 under Hydrothermal Conditions

The hydrothermal synthesis of the large-pore oxy-fluorinated gallophosphate ULM-5 has been followed in situ using time-resolved energy dispersive and angular dispersive X-ray diffraction. A variety of synthetic parameters such as temperature, reagent stoichiometry, source materials, and pH have been studied, and their effect on the crystallization determined. The nature of the phosphorus source used, either orthophosphoric acid or phosphorus pentoxide, is found to have a profound influence on the reaction pathway. Using orthophosphoric acid, ULM-5 is found to form very rapidly following a short induction period. A kinetic analysis of the crystallization of ULM-5 using orthophosphoric acid under isothermal hydrothermal conditions has been performed. Comparison of the experimentally determined extent of reaction (R) versus time data with those predicted by various theoretical models indicates that over a wide range of temperatures and pH the crystallization can be modeled by a three-dimensional diffusion-controlled process. This process occurs at a rate essentially independent of temperature and pH. In contrast, using phosphorus pentoxide, the formation of ULM-5 is found to proceed via the formation of either of two distinct crystalline intermediate phases, which subsequently react to form the ULM-5 final product at a rate which is strongly dependent on temperature. The relative quantities of each intermediate phase formed depend critically on the precise reagent stoichiometry used. Conditions have been identified in which ULM-5 can be formed exclusively via either intermediate phase. The mechanism of transformation of intermediate to product phases appears to be either a direct solid- solid transformation, or via the dissolution or amorphorization of only a small quantity of material at the surface of the intermediate crystallites.

Oxyfluorinated compounds with open structure XI. Interaction between the ULM-3 type framework and linear diamine templates of different chain lengths studied by X-ray diffraction and solid-state nuclear magnetic resonance characterization

The synthesis and structural characterization of oxyfluorinated microporous gallophosphates with the ULM-3 type are presented. This material is hydrothermally prepared (180°C, autogenous pressure, 24 h) by using linear diamines [H 2N(CH 2) 3–5NH 2] as templates. The structures of the phases obtained with the variable organic chain lengths were examined by single-crystal X-ray diffraction (XRD) and 31P, 19F, 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. This study showed that the relative flexibility of the C 3C 5 diamines allows the preservation of the topology of the type ULM-3. In this series, the presence of fluorine, which is found in the bridging position between two gallium atoms, is strongly correlated to the existence of hydrogen bonds with ammonium groups of the organic molecules.

Hydrothermal synthesis and crystal structure of the microporous gallophosphate [NH4]4[Ga8P8O32(OH)4(H2O)4]·4H2O·0.64PrOH with an octahedral–tetrahedral framework

The new microporous gallophosphate, [NH4]4[Ga8P8O32(OH)4(H2O)4]·4H2O·0.64PrOH, has been synthesised and structurally characterised; it has a framework isostructural with that of [NH4][Al2(OH)(HPO4)2]·2H2O. The gallophosphate consists of gallium-centred octahedra (GaO6) and phosphorus-centred tetrahedra (PO4) which together serve as basic building units to form a three-dimensional framework structure. The gallophosphate crystallises in monoclinic symmetry with space group P21/n, a= 9.6814(0), b= 9.6568(0), c= 9.7618(0)Å and β= 102.90(5)°. The structure possesses three-dimensional channels with eight-ring windows running along the [100], [010] and [001] axes in which organic template molecules and inorganic NH+4 cations in pairs are located.

Aspects of the characterization of cloverite by solid-state n.m.r. techniques

Microporous gallophosphate cloverite has been studied by multinuclear ( 13C, 19F, 31P, 71Ga) solid-state n.m.r. spectroscopy. An extraordinarily strong quadrupolar coupling is shown to be the reason for a misleading line shape in 71Ga MAS n.m.r. spectra. Using static 71Ga n.m.r. spectroscopy, an estimate of the size of this quadrupolar coupling can be obtained. The limitations of the MAS technique for the study of quadrupolar nuclei in sites with very large quadrupolar couplings are addressed.

Solid-state NMR investigation of the novel microporous gallophosphate cloverite

The investigation of the gallophosphate molecular sieve cloverite by solid-state 13C, 31P, and 71Ga NMR techniques is described. Comparison of the 13C CP/MAS spectra of cloverite quinuclidine and quinuclidinium chloride give further evidence that the templating amine is protonated. The non-spinning CP experiment shows the full chemical shift anisotropy and reveals no motion of the template molecules. The 1H-decoupled 31P MAS spectrum of cloverite exhibits very poor resolution. However, the resonance lines of the five crystallographically independent 31P atoms are resolved by applying a dipolar-dephasing technique which utilizes differences in dipolar 31P—1H interactions. CP/MAS experiments with variable contact times and a depolarization experiment support this result and allow partial assignment of resonance lines to two groups of 31P atoms. The experimental conditions for 71Ga CP/MAS experiments were evaluated using Ga2(SO4)3·18H2O as a model substance. Application to cloverite with decreasing contact times shifts the maximum of the main signal from − 41 to − 26 ppm, thus indicating the presence of gallium sites with different cross-polarization dynamics.

Synthesis and characterization of cloverite: a novel gallophosphate molecular sieve with three-dimensional 20-membered ring channels

Cloverite, a novel cubic microporous gallophosphate, with three-dimensional channels circumscribed by 20-membered rings in the shape of a four-leafed clover, was synthesized in the presence of fluoride ions and quinuclidine. It is stable to at least 500°C in a dry atmosphere and shows high adsorption capacity for n-hexane, xylene, and mesitylene. By 13C n.m.r., it was found that quinuclidine is protonated, thus compensating the negative charge of fluoride located in the double four-rings. The 31P and 71Ga MAS n.m.r. results are in agreement with the crystal structure analysis.

Directing Effect Of Fluoride In The Synthesis Of Molecular Sieves With New Characteristics And Of The First Twenty-Membered Ring Microporous Solid

ABSTRACTThe directing effect of fluoride anions in the synthesis of molecular sieves seems to be related to the strength of its interaction with the framework. For example, whereas F is bridging 2 Al atoms of a four-membered ring in AlPO4-5 containing tetrapropylammonium fluoride and in an new triclinic morpholine-containing chabazite-like AlPO4, it is found in double four-rings in three other phases which were synthesized recently. Firstly in the tetragonal all-silica AST-type octadecasil (space group I4/m, a = 9.194(2)Å c = 13.396(4)Å) which was obtained in the presence of quinuclidine and HF. Secondly in two novel cubic microporous gallophosphates which are formed selectively in the presence of hydrofluoric acid. One has the structure type LTA (space group Fm3c, a = 24.0354(1)Å) and crystallizes with di-n-propylamine as a template, and the other shows a novel structure type (space group Fm3c, a = 51.84Å) with a 3-dimensional 20-membered ring channel system. This is the largest membered ring ever reported for a synthetic material.

A novel mixed octahedral–tetrahedral framework: X-ray characterization of a microporous gallophosphate, Ga2P2O8(OH)H2O·NH4·H2O·0.16 PrOH (GaPO4-C7)

The structure of the microporous gallophosphate, Ga2P2O8(OH)H2O·NH 4·H2O·0.16 PrOH, consists of gallium-centred octahedra and phosphorus-centred tetrahedra as basic building units to form three-dimensional channels with the 8-ring running along the a,b, and c axes in which NH4+ cations are located in pairs.